1. Field of the Invention
This invention relates to electronic multiplexing circuits for conducting multiple signals from one equipment to another and more particularly to a novel multiplex system for controlling remote receivers by employing a single pair of wires carrying digital coded power line signal for a brief interval.
2. Background of the Prior Art
In the past, it has been common practice to place a plurality of signals on a single wire or a pair of wires, such as coaxial cable, for the purpose of transmitting the multiple messages to a remote location. By employing frequency division techniques, a great many messages may be placed on a single wire for transmission. Such a procedure is often used in a variety of telemetering networks.
However, difficulties and problems have been encountered with prior industrial multiplex and telemetering systems employing coded tones superimposed upon the power line which stem largely from the fact that it is difficult for the circuits to insure against false operation in the event of voltage spikes or other spurious or false signals. These undesired voltage spikes or transients are generally associated with heavy inductive loads, such as solenoids, multihorsepower motors, or the like coupled on the same circuit or particularly in the instance of the presence of lightening. The unwanted voltage spikes or transients have the undesired effect of operating the remote equipment when it is not desired to have such equipment in operation.
Therefore, a long standing need has existed to provide a properly designed multiplex system having transient signal immunity and which will conduct control signals for both information and power on the same wire or line.